Electron optics



ELECTRON OPTICS Filed July 8, 1956 INVENTORS MAX KNO LL RUDOLF URTEL BY Patented Mar. 28, 1939 UNITED" "STATES ATENT oFsicE assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. BL, Berlin, Germany Application July 8, 1936, Serial No. 89,680

' In Germany July 8, 1935 1 Claim.

Thisinvention relates to electron optics, and in particular, to means and methods of constructing cathode ray tubes which are short and yet exhibit the same deflection sensitivity as longer tubes.

This invention solves the problem of constructing a cathode ray tube which may be used for the purposes of television, i. e. a cathode ray tube which can be used either as a scanning means on the transmitter side, or as picture composing device on the receiver side, in which the length of the tube is as short as possible, and to give a high deviation sensitivity of the cathode ray beam at the same time. These two requirements contradict each other at least insofar as a high deviation sensitivity of the cathode ray beam can be attained by a correspondingly long path prescribed by the ray at its state of deviation. Therefore if at a high deviation sensitivity a short tube is to be obtained at the same time, other means are to be resorted to than the lengthening of the path prescribed by the ray following the deviation thereof, i. e., other means are to be applied than the lengthening of the so-called pointer length. The saving on tube length therefore, can only be accomplishedin case of a predetermined pointer length in that those paths which aside from the pointer length furthermore figure in the total length of the tube are shortened as much as possible. These paths consist of the distance of the cathode ray generating system from the ray concentrating device and the distance of the ray concentration device from the ray deviating device. However, also this reasoning does not readily lead to a cathode ray tube having a length of such shortness as is desirable for commercial television sets.

It might be considered on first thought that the distance between the cathode ray generating system and the ray concentration device cannot be selected solely with the View to a possibly short tube length, but that the diameter of the luminous spot which depends upon the dimensioning of this distance must also be taken into consideration. As a matter of fact, for concentration devices for cathode rays similar laws prevail within certain limits as in the case of an optical concentration lens for lightrays. Hence if a diameter of a luminous spot is to be achieved with a sufiiciently small size, and this is necessary in case of television images with a large number of lines, and this also at a comparatively large picture surface, the distance between the cathode ray generating system and the concentration device cannot be shortened by any desired amount,

since (in the same manner as in case of the proportion between picture size and size of the objective in an optical concentration lens) the proportion between the diameter of the luminous spot and the size of the source of electrons be- 5 comes the greater the higher the ratio of the distance between concentration device and luminous screen to the distance between electron source and concentration device. In fact in order to at tain the necessary intensity in the luminous spot the electron sources employed must not be too small, and furthermore it should be bornein mind that the distance between the concentration device and the deviation arrangements cannot be shortened by any desired amount for any type of concentration device which, as such, may consist of a magnetic or electrostatic electron lens, and likewise not for any type of deviation arrangement, which may likewise be of a magnetic or electro-static nature.

In the case of combined magnetic electron lens and magnetic deflection means, the limiting factors which determine how much the tube may be shortened are, first, the physical dimension of the coils, and secondly, the physical configuration of them. The first factor is important because the size of the coils determines the minimum distance which the deflection coils may be brought into proximity with the focusing coils, since obviously, the two windings cannot occupy the same space simultaneously. The second factor is important due to the fact that the concentration effect of the usual magnetic lens is not restricted to the immediate volume occupied by the coil, but rather, extends to some distance on either side of the coil, as will be appreciated from the configuration of the lines of force of a solenoid as is well known in the art. These factors, therefore, inhibit the production of a tube from being as short as is desired.

In like manner, the combination of a magnetic lens with an electrostatic ray deviating device, i. e. with deviation plates, does not afford placing the deviation plates so near to the magnetic lens as in the arrangement according to the invention and which will be described later on, for the immediate reason that, as already pointed out, the cathode rays, even after leaving the concentration coil are still subjected to the action of the coil field, so that they must not as yet be deviated, if a sharp luminous spot is to be obtained.

When using an electrostatic concentration lens and deviation plates at the same time, the distance between lens and deviation device can likewise not be shortened at will, since the plates represent equi-potential surfaces which do not correspond to those of the lens field, so that the formation of a lens field would produce a disturbing effect.

Only if, as proposed in accordance with the invention, an electrostatic concentration lens is used in conjunction with magnetic ray-deviation arrangements, i. e. with deviation coils, will it be possible to decrease the distance between the lens and the deviation arrangements to a wide degree, and in this case it is even possible to arrange the electrostatic lens entirely or partially within the deviation coils, so that so to say, a negative distance will be obtained between the concentration device and the deviation arrangements.

Turning now to a more detailed explanation of our invention, attention is directed to the drawing in which:

Fig. 1 shows schematically one embodiment of the invention, and

Fig. 2 shows a modification of the invention.

A mode of construction of such arrangement is schematically shown in Fig. 1 of the drawing. Herein is item I a lens electrode whose left end, not shown, is connected to the anode of the cathode ray tube, and which would have a potential of, for instance, +2000 volts relative to the cathode of the tube. The lens furthermore, has an electrode I I having a potential of, for instance, +500 volts relative to the cathode, and also a further electrode I2 connected to the conductive inner layer of the conical tube part, and which has the same potential as the electrode ID. The deviation coils of which only the one coil pair I3, I4 is shown, surround the lens, so that the field formed between the electrodes II and I2 lies within the coils.

A further reduction in the length of the tube can be achieved in accordance with the invention, in that among the numerous electrostatic lenses possible, that type is chosen in which at the lens electrodes with an increase in distance from the cathode, increasing positive potentials exist, 1. e. a so-called acceleration lens. In this case, according to the teaching of the geometric electron optics, the distance between the electron source and the electron lens can still be reduced below the value corresponding to the distance between electron lens and luminous screen, and this without increasing the diameter of the luminous spot at the same size of the electron source, and which is of essential importance to the problem of providing a short tube length.

A mode of construction according to the invention and the use of an electron lens of this last mentioned type is schematically represented in Fig. 2 of the drawing. Item I5 designates herein the glass wall of the tube, and I6 and H are two lens electrodes. The electrode I6 is understood to have the left end connected to the plate of the tube, and may have a potential for instance of +500 volts relative to the cathode. The electrodes which may, as in the case of the electrode I2 in Fig. 1, be connected to the current conducting inner layer of the conical tube part, have a potential of for instance +5000 volts relative to the cathode. The lens field is formed approximately in accordance with the equi-potential surfaces as shown in dash lines, and this field lies with its major portion within the deviation coils I3, I4, since it reaches practically into the electrode I'I approximately at a distance equal to the smallest diameter of these electrodes.

Since, as already stated, it is not possible to increase at will the distance between the deviation coils and the luminous screen with the view of obtaining a short tube length, other auxiliary means shall further be provided according to the invention, in order to attain a high deviation sensitivity of the tube. To this end, the deviation} coils are arranged about the tube neck directly at the start of the cone frustrum-shaped tube part at the tube neck, as shown in Fig. 2. The provision of the coils on the tube neck assures a high strength of the deviation field in the tube axis and in the vicinity of the tube axis, and since the cone-shaped part of the tube begins directly in back of the deviation coils, the deviated ray passes almost entirely through a tube portion having a sufiiciently wide diameter. Hence, it is possible to dimension the tube neck without regard to the space required by the deviated ray, a condition favorable to the field strength of the deviation field in the tube axis and vicinity of the tube axis, thus contributing to the deviation sensitivity of the tube.

It will be appreciated that the drawing does not show the usual cathode Wehnalt cylinder, the fluorescent screen, or modulating grid since the invention is directly related to the use of magnetic deflecting coils acting in combination with an electronic lens but which coils are placed in juxta-position to the plurality of anodes used in the electrostatic electronic lens system. Since the elements not shown are well known in the art, as well as their positioning with respect to the anodes shown, it is felt that it is unnecessary to show or describe these in detail. It will further be appreciated that the magnetic deflecting coils may be supported within the tube in methods well known to the art so that the electronic lens system and deflecting system may be built as an integral unit and placed within a glass envelope. This mode of construction has the advantage that the deflecting coils I3 and I4 are held in fixed relationship with respect to the electron system and do not require adjustment after the tube has been assembled. On the other hand, mechanically the problem is simplified by placing the deflecting coils exteriorly to the lens system as shown in Fig. 2.

Having described our invention, what we claim is:

A cathode ray device comprising means for producing an electron beam, an electrostatic electron lens having two principal planes for focusing the produced electron beam upon a predetermined impact plane spaced from the electron beam producing means and electro-magnetic means for deflecting the electron beam, said electro-magnetic means being positioned in the region of said principal planes and having the maximum field intensity within the region of said planes.

MAX KNOLL. RUDOLF URTEL. 

